1. Technical Field
The present invention relates to the production of a spiral shaped puff extrudate and, in particular, to confining the extrudate in a tube or like peripheral containment vessel while applying a force or resistance on the extrudate downstream of the extrudate's glass transition point. The downstream force or resistance causes the otherwise linear extrudate to “back-up” into the containment vessel, thus coiling into the spiral or curl shape.
2. Description of Related Art
The production in the prior art of a puffed extruded product, such as snacks produced and marketed under the Cheetos™ brand label, typically involves extruding a corn meal or other dough through a die having a small orifice at extremely high pressure. The dough flashes or puffs as it exits the small orifice, thereby forming a puff extrudate. The typical ingredients for the starting dough may be, for example, corn meal of 41 pounds per cubic foot bulk density and 12 to 13.5% water content by weight. However, the starting dough can be based primarily on wheat flour, rice flour, soy isolate, soy concentrates, any other cereal flours, protein flour, or fortified flour, along with additives that might include lecithin, oil, salt, sugar, vitamin mix, soluble fibers, and insoluble fibers. The mix typically comprises a particle size of 100 to 1200 microns.
The puff extrusion process is illustrated in FIG. 1, which is a schematic cross-section of a die 12 having a small diameter exit orifice 14. In manufacturing a corn-based puffed product, corn meal is added to, typically, a single (i.e., American Extrusion, Wenger, Maddox) or twin (i.e., Wenger, Clextral, Buhler) screw-type extruder such as a model X 25 manufactured by Wenger or BC45 manufactured by Clextral of the United States and France, respectively. Using a Cheetos like example, water is added to the corn meal while in the extruder, which is operated at a screw speed of 100 to 1000 RPM, in order to bring the overall water content of the meal up to 15% to 18%. The meal becomes a viscous melt 10 as it approaches the die 12 and is then forced through a very small opening or orifice 14 in the die 12. The diameter of the orifice 14 typically ranges between 2.0 mm and 12.0 mm for a corn meal formulation at conventional moisture content, throughput rate, and desired extrudate rod diameter or shape. However, the orifice diameter might be substantially smaller or larger for other types of extrudate materials.
While inside this small opening 14, the viscous melt 10 is subjected to high pressure and temperature, such as 600 to 3000 psi and approximately 400° F. Consequently, while inside the small orifice 14, the viscous melt 10 exhibits a plastic melt phenomenon wherein the fluidity of the melt 10 increases as it flows through the die 12.
It can be seen that as the extrudate 16 exits the orifice 14, it rapidly expands, cools, and very quickly goes from the plastic melt stage to a glass transition stage, becoming a relatively rigid structure, referred to as a “rod” shape if cylindrical, puffed extrudate. This rigid rod structure can then be cut into small pieces, further cooked by, for example, frying, and seasoned as required.
Any number of individual dies 12 can be combined on an extruder face in order to maximize the total throughput on any one extruder. For example, when using the twin screw extruder and corn meal formulation described above, a typical throughput for a twin extruder having multiple dies is 2,200 lbs., a relatively high volume production of extrudate per hour, although higher throughput rates can be achieved by both single and twin screw extruders. At this throughput rate, the velocity of the extrudate as it exits the die 12 is typically in the range of 1000 to 4000 feet per minute, but is dependent on the extruder throughput, screw speed, orifice diameter, number of orifices and pressure profile.
As can be seen from FIG. 1, the snack food product produced by such process is necessarily a linear extrusion which, even when cut, results in a linear product. Consumer studies have indicated that a product having a similar texture and flavor presented in a “curl,” “spiral,” or “coil spring” shape (all of which terms are used synonymously by Applicant herein) would be desirable. An example of such spiral shape of such extrudate is illustrated in FIG. 2, which is a perspective view of one embodiment of a spiral or curl shaped puffed extrudate 20. The embodiment illustrated in FIG. 2 is an extrudate with a relatively tight pitch, short diameter, and cut at approximately four turns or spirals. It should be understood that when referring to a curl, spiral, or coil spring shaped puffed extrudate, however, Applicant intends that the pitch (which can be a left hand or right hand pitch) and diameter of the curl or spiral in addition to the rod (or other shape) diameter and piece length can each vary independently to provide a wide variety of products. Unfortunately, the high volume process described above provides unique challenges in producing such shape 20.
The usual method for imparting a spiral shape in an extrudate, such as with spiral shaped pasta, involves forcing the dough through a spiral shaped die orifice. As can be readily understood, such solution would not work with a puffed product that is in a plastic melt stage inside the die and produced at the velocity described above, since the product would have no memory of the imparted spiral shape upon exiting the die. In fact, it has been found that it is extremely difficult to meaningfully manipulate the melt as it passes through the die in order to induce an extrudate to wind in free space, by, for example, a temperature differential from one side of the die to the other, without substantially reducing the flow rate of the melt through the die.
Another prior art method for imparting twists or curls in the dough involves using an extruder with rotating nozzles. This process, however, is only viable when the extrudate retains a very pliable form. Further, extrusion by way of rotating nozzles typically, again, requires a greatly reduced throughput rate as compared with the relatively high volume production desirable with the prior art linear products.
To further complicate the matter, a larger surface area is required on the extruder face for the same number of individual dies when extruding a curled product versus a linear product, since the space between each die as between a linear product and a curled product must necessarily be increased to allow for the diameter of the spiral. By way of example, an extruder face may under prior art conditions accommodate 28 individual dies running at 80 lbs. per hour per each die, thereby producing a 2,240 lb. per hour throughput for the entire extruder. In order to theoretically produce the curl shaped extrudate 20 shown in FIG. 2, the same extruder face might only accommodate, for example, 4 individual dies. By way of further example, if it is necessary to slow the throughput rate to less than 30 lbs. per hour per die in order to impart some spiral shape on the extrudate by manipulating the melt inside the die, this reduces the total throughput for that extruder to only 120 lbs. per hour. Thus, by converting an extruder to manipulate the melt inside the die and imparting a spiral shape, the extruder maintains only about 5% of the throughput rate as compared to the standard linear production, even though the throughput for each individual die is reduced to about 38% of the previous throughput rate. The problem becomes even more pronounced if the extrudate throughput is reduced to even lower levels.
It can be easily understood that any prior art solution that requires the substantial reduction in the throughput of the extrudate, therefore, is not an acceptable alternative when, for example, twenty extruders must be used to match the throughput of a single extruder when compared with a linear production line. Forcing the extrudate into some spiral shaped former upon exiting the die is also not practical due to the brittle consistency of the extrudate after it drops below its glass transition temperature. Also, such spiral shaped former could become easily clogged, thereby requiring stopping the entire production line.
Consequently, a need exists for developing a method and apparatus that can impart a spiral or curl shape in a puff extrudate while also maintaining an efficient throughput rate of the product through the extruder. Ideally, such invention should be readily adaptable to existing extruders and dies, require little or minimal modification to such equipment, allow for traditional face cutting, and introduce as few collateral processing issues as possible when integrated into the overall production line.